Response to Predation by Colonies of the Florida Harvester Ant, Pogonomyrmex Badius

Abstract

The effect of predation (by the systematic removal of forager ants) on the behavior and population structure of Pogonomyrmex badius colonies was studied during the summer of 1965. For 23 wk, 50 workers per day were removed from one group of 10 colonies and 10 ants per day from another group of 10 colonies. Another 10—colony group served as a control. No effects of removal were observed in the 10/day group. Within a week after removal began, aboveground activity was reduced drastically in many of the 50/day colonies and the removal of a complete sample each day was impossible. Later, colonies underwent extended periods (3 wk or more) of complete inactivity aboveground. The mean dry weight of workers removed at the rate of 10 per day increased over the removal period. The mean dry weight of workers removed at the rate of 50 per day increased for the first 9 wk and then decreased rapidly over the rest of the removal period. As removal continued, craters became smaller and many disappeared; nest entrances were shifted under the overhang of grass clumps and were covered with dried leaves. Intercology conflicts became common at most 50/day colony sites. After the 23—wk removal period, five colonies from each treatment group were randomly selected for excavation. Significantly fewer ants were excavated from both the 10/day and 50/day colonies compared to the controls. Significantly more ants altogether were produced (removed plus excavated) by the 10/day and 50/day colonies. However, the increase in the number of ants produced could not immediately counteract the loss of the ants to aboveground removal. At excavation, workers in the 50/day colonies weighed less than those in the control and 10/day group. In each treatment group, workers collected from the top 20 cm of the nest system weighed less than those collected from the remainder of the nest system. Also, in the 10/day group, workers collected at the surface during the removal phase weighed less than those present in the top 20 cm of the nest at excavation. No such difference existed in the colonies of the 50/day group. By midsummer of the next year (1966), the remaining experimental colonies appeared to be back to normal strength. Although the forager population was greatly reduced, the colonies were able to survive until more foragers could be produced. Such an adaptive strategy is possible because of a highly developed social behavior which results in a well—defined division of labor within the ant colony.

Mortality risk versus food quality trade‐offs in ants: patch use over time

“…However, researchers have often concentrated on only one aspect, such as food collection (Taylor, 1977;Davidson, 1978;Fowler, 1987;Holdcr Bailey & Polis, 1987) or the response t o above-ground predation risk (Gentry, 1974;Whitford & Bryant, 1979;Shaffer & Whitford, 1981;MacKay, 1982;Munger, 1984). These studies have added greatly to our understanding of ant ecology, but, as pointed out by Gordon (1989, group properties of colonies may be obscured or even erroneously predicted when behaviours or tasks are considered in isolation.…”

“…Simulated predation of workers from the area surrounding nest entrances can result in the cessation of foraging activity by Pogonomyrmex and Myrmecocystus species (Gentry, 1974;Whitford & Bryant, 1979;Shaffer & Whitford, 1981;Munger, 1984;Gordon, 1986). Predation at nest entrances may even lead to total cessation of above ground activity.…”

Invitation Paper (C.P. Alexander Fund): Foraging of Individual Workers in Relation to Colony State in the Social Hymenoptera

“…This occurs because smooth transfer of nest building materials from one worker to the next affects waiting times and influences the relative timing of the different work cycles for foragers and cell builders. In many cases, the number of sexuals produced by a colony is an increasing function of colony population size up to a point (Michener 1964;Gentry 1974;Pomeroy and Plowright 1982;Elmes and Wardlaw 1982;Seeley 1985;Seeley and Visscher 1985;Lee and Winston 1985a;Johnston and Wilson 1985;Miiller and Schmid-Hempel 1992).…”

On Caste Ratios in Ant Colonies: Population Responses to Changing Environments

“…Secondly, some workers have shown that among mature colonies, worker morphology varies with competition (Davidson, 1978) or predation pressure (Gentry, 1974). In addition, rather rapid monotonic changes in the caste structure of a given colony may be effected by experimental manipulation (Gentry, 1974;Passera, 1974). This paper reports a new type of response by ant colonies to changing environmental parameters.…”

“…First, it is well known that, during the colony life cycle, size and weight of workers undergo transitions from an initial group of small, undifferentiated workers to the full caste complement of the mature colony, whose workers are routinely larger and, for some species, highly differentiated (Oster and Wilson, 1978). Secondly, some workers have shown that among mature colonies, worker morphology varies with competition (Davidson, 1978) or predation pressure (Gentry, 1974). In addition, rather rapid monotonic changes in the caste structure of a given colony may be effected by experimental manipulation (Gentry, 1974;Passera, 1974).…”